Electric furnace



March 3.1, 1931. G, KELLER 1,798,678

ELECTRIC FURNAC E Filed June 20, 1927 2 SheetsSheet l 15 @f f!- J5 MAM .E 57 l I l l Y W I E i I W r 722 A I g Tv W I i @A GI gf GI t Z0 65A Z162" a Z i? '6g @ag/Wr m6, (fobj ig/f March 31, 1931. G. KELLER 1 1,798,678

ELECTRIC FURNACE Filed June 20, 1927 2 Sheets-Sheet 2 @WML glu-lli www All implication. lec June SE1?, N2?,

to electric ,furnace Fllliis invention relates s e llas among its obglects of tlie resistor typ l c improvements in the construction andcp^r ation oit suoli furnaces. According; e

elements of furnaces of the foregoing type are so arranged il operated as 'to prevent, as muoio. as pessil e, sudden fluctuations of the liest input into the furnace. Un tbe contrary, the neat in the furnace is maintained as neuerL possible equal to tlie beat requirements of e turna e during each rnc nient of the oper n thereon The invention i i. i be best understood from e lowing descriptions oezemplieetions hereof, reference being' had to the accorm partying; drawings wherein Fig. l illustrates diagrammatically the arrangement and operation of a Vfurnace accordiig to my invention.

Fin, 2 is a curve diagram illustrating ltice temperature conditions during the furnace operation and 3 is a View similar to Fig. 1, illustrat- 'ing another form of the invention ln the operation of electric furnaces of the resistor type, such as are used `iter heat treatment, etc., the electrical input must be'go'verned by the maximum allowable surface v'temperature of the charge, by the timerequired to bring up the entire body of thev charge to the desired temperature, and by the soakingl period during which the charge is desired to be maintained at a particular temperature. In lthe practical operation of furnaces, thev foregoing recquirements with respect to the temperature control in the :turnace impose serious diliculties in 'the Way of manufacture and operation, Thus the observance'of an upper temperature limit at the surface of the charge places a restriction on the amount of energy that may be supplied 'to the furnace. On the otherxliand, economy of operation makes it necessary to carry out the process in as short a time as possible, and

as a result requires the use of the largest posl sible amount of power for beating the urnace. As far as I am aware, heretofore the foregoing contradictory requirements have "0 been, to a certain extent, met by supplying rical in ctn r tently, tne

y so

riofl and ig e desired l, the numbe; l" between 'aeetemnerature of tn ceederla Tile foregoing prior art type operation lies rlisadyant """be conti u -1 .1 a connection and disconnection relatively large power flow places e errlinarily heavy demands on t e circuit i, uwlrers, particularly in heat treatment iu es of larger size, uli-ere the 'full power only be interrupted with the aid of compleateeland costly switch apparatus, :if an attempt is :made to reduce the number of switching operations by lengthening the beating p 'od and the intervals therebetrveemtlie diileronce between the .minimum and ,munir temperatures Within the furnace rapir ly becrnnes Very large, `meetingYarmtlier limitation for this type of operation. y

The periodical disconnection and reconnection of large powenconsurning apparatus means also a succession .of peek loads on the electrical supply line ci ylie furnace. This 'has not only a liiglnly clic-,turbingga iniluenceon the remaining load connected the line, such as lights, but yery often reacts unlavorably on the power station itself, .'Wnicli, in many instances, penalizes consumershaying such periodically Varying power demands.

According to my invention, the contradictory requirements with respect tothe 'furnace operation are met much better than in the foregoing prior art arrangements Aand systems of operation by making the power 1n'- put, 1into the 'furnace continuous instead of intermittent, and arrainging` that the electrical power supply shall be controlled in accordance with the energy streams in 'the furnace. Considering 'for 'the moment 'the enorgy 'How conditions in the furnace at the time after the charge has reached its maxitween the interior anni the exterior of the furnece chernben The other streein oi? energy 1s represented the heet rfiowing from the exterior surface the charge into the interior thereof. 7iihis charge stream varies in niegnitniie en ciepenos on the momentary' temperature conoiim tions of the charge it is irirgest the beginning snfiv decreases in the course of the nesting processs The energy thet to be siippiie. to the furnace is thus compose@ of two items, one that is constant enti corresponcis to the ioss energy, emi one that is yeriebie enti corre? spon de to the energy iiowing into the charge. According to the invention7 Jnfurnaces oi the foregoing type ere so errsngerienci operated that the eiectricei energy is snppiiec to the furnace sn'bstentisiiy continuously, anni so controiieri that after the maximum. permissibie surface temperature of the charge has been sttaine, the 'power input et everyv instant is maintains@ sensi or epprorirneteiy equai te the -snrn oi the fnrnece iosses anni the ernennt oi' energy which iows into the interior oi: the charge when the surface terne persture is et the maximum permissible veine. To this en provisions ere niscie for controiiing the power suppiy in eccorsnce with the temperature cenriitionss both outsicie inside the charge. the preferred arrangement this is 'secure without interrupting the current iiow into the furnace. It is eiso eimeci to continuonsiy ntiiize sii the heating eiernents of the furnace so that the disconnection of inciiyiduei elements is avoidedu s Where the resistor furnace is supplied from a three-phase system coarse and ine adjustifient oi? the heet fiow into the furnace may be reediiy obtaine es follows: for

coarse adjustment the hee-ting elements are .connected either in richte` or in star; ne ad- Lreepere a. charge l1, that is to be treated. A peil' of pyrometer elements u enci o, in the form of thermo-'couples are errsngeci to respond to the temperature at the surface of the charge and in the interior thereof, respectiveiy. The resistors Ai, etcw El, etcL, are arranged to. be supplied from threephese bus-bers l2 that may be connected. through e main circuit breaker i3 to e. poiynhsse snpniy line i4. The circuit breaker is errengesi to be ectuete; by operating eoii l5; The resistors the heating group are srrengeri to be controiiefi by ineens ci a, three-pcie cubie-throw switch 2i emi rney be connecteci her in site scross the bus-bers 1Q by throwing the switch 2l to the tops or in ster by throwing 'the switch down The switch 2li. is operated Crem en ectneting coii The resistors oi e i ester group B rney be siniiieriy connectee -n ster or in site across the bus-bers ineens oi e' three-noie fioubie switch that is arranged to be operate j 2li, ncinciec 'the ster connection o? the iirst mentioned heater ys e threephese induction reguietor 25 haring primary windings 36 connectedL ross the hns-bers end secondary windings n] connected to the iower terinineis of the threonoie switch 2i., -threepois switch 28 incinderi in. the connection between. the resistor eieinents er the second group and the hns-bers serves to oie-energize or energize sei group 7Ehe sctnsting coii switch 2S is arranged to' be cioseci or opened i byrneens @sir of actuating coiis 29 enoi 29 The switches 2i, 23 and 28 are controilel by the sbove rnentioneri thermo-coupies u end e in orcier to secure within the ifnrnece and the charge the ciesireci temperature conditions. To this end each of the thermo-cow pies u, e, operates e regnieting device i7, respectiwiy7 which in turn controis the operetion oi the ser/crei switches through relays Si? 32,33, The reguieting device has e mor/:ibis Contact erin 'Ui moved in accordance with the eiect oi the temperature on the outer thermo-coupie e; end three contact members u2, 'm3, wi, for energizing reieys 317 327 and the cut-out eoii 29 of the fiisconnecting switch 28 of the second resistor group respectively, the energy for seioi reieys andcoii being supplied `ironi the secondary winding of an auxiliary transformer 35. Simiieriy, the regulating device V has e. movable contact arm Vl actuete in accordance with the temperature ci: the internati thermo-Connie v and three Contact members e2, e3, 114.-, for energizing the closing coil 29 or the disconnecting switch 28, the cut-out coii 2W of seid switch and the relay 33, respectiveiy. The latter reieys when ciosed, estebiishes e circuit for energizing the cut-out coii 15 of the main switch 13, thereby isconnecting the supply from the furnace.

The resistors o the heater group A ere so Lim-am@ va; th@ energy f. sta-1f, is, ap L; su ,mism '1Z0 0mm the -en- SGS@ @mimmo-ici.,

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cmmeced "be L m stars Wu, @mmanwmperagum Y 1 @barge 23 being udg, Tela *mh iow luto l o2; in @marge nommen #ma t@ y V, T A; the gamma A sperm@ in QL wlmeeton.,

is point C @ufl above? the bhs resister group are suck needl im my Wi just .@jbu, supply the w25 assuming haf',

' 'ille Eine, ih@ power inputs 0 -ing a, power input 01W@ Vthe thermo-enum@ in arde? he Can '35 ber affecting pymmetf @a me s" arm has um: z unzfa t@ es" causing the resistance @Qmmc to me Hm; pemtufe me chal .fb th@ maximum arm moves $0- 'dw @en theyeby spelling the discoand cuzig Ox the Seco-mii f supply somma l'f the im stm wntnues izo p;s@7 owe l mum. is exceeded, aha commu am?, T mames into conta@ with th@ c I fv. This operages the mls@ hrougl effects the dsscmnf bays 'by means switch X3,

off En@ @Miva suppy izo L LUIS $5 may? am metan@ wia@ p ai; pim';

unnamed m f Th power input @uwe "w" @he 'power supplied me reduced in sma Sp tion it is nend 'f' fesistgr group A sha mi for emmectng Sim egwlang device to tha eibd from the internal thernlwmup fv; and im ample-r 44 cspossz in. the connecticn between the refgulatimg devies 'L-E52 and Juw Seizure the die sx'el eguatng effect with fthe @mamut of regulating energy that may be derived troni a thermo-couple.

.connected to the regulator 42. The switch 43 for connecting the induction motor regulating device 42 to the thermo-couple o is operated loy an actuating coil 45 which 1s energized by the relay 3l when the resistor group A is connected in star, .an additional switch 46 being included in the energizing circuit of said coil Li5 in order to permit the action oi the induction regulator to be cut od at will.

W ith the 'foregoing arrangement the induction regulator is directly under control of the internal temperature of rthe charge from the moment the resistor group A is connected in star. As long as the internal temperature is hel'ow the desired value, the induction regulator will boost the voltage, gradually reducing the voltage as the temperatur-e of the interior approximates the external 'temperature. `With this arrangement iine adjustment ol the power supply to conform to the particular requirements. may loe secured. li the temperature 'tends to rise above the permissible Value, the induction regulator will automatically reduce the voltage to preventf'such rise.

In the alcove described example, the rarious switches, relays, etc., have heen indicated diagrammatically, as the precise structures oi the relays and switches, do not constitute the suioj'ect matter ci the present invention and anytype ci switches or relays that will operate in the way described above may loe used in a way familiar to those skilled in the arto The gradual variation of the power supplyin accordance with the operation oi each thermo-couple, lay controlling a suitably connected induction regulator, may also be embodied in an arrangement wherein the induction regulator is under control both of the internal aswell as .ci the external thermocouple. Many other arrangements of apparatus may also he employed to carry'out, with more or less rnodicetions of the above descrihed arrangements, a method oi operation involving the tine and coarse regulation of the power supply to a resistor `urnace in accordance with the temperature conditions thereof, under elimination of complete interruption or the power supply as practiced heretofore..

The alcove described system of furnace regulation lends itself also for partial application, that is, for comhination with systems 'ci the type used heretofore, that is, combination oi continuous and automatic power regulation with intermittent power supply. Thus, during one part ci the heating process energy may he supplied connuocere tinuously with gradual or step-loystep decrease ci" the power input until the internal temperature has reachedthe limiting value. Thereafter the power supply is controlled hy intermittently cutting od the power to maintain the desired temperature. `With such arrangement the energy conveyed to the furnace during the iirst portion of the lprocess must he maintained equal to the sum oi the loss of energy and oi the energy corresponding to the heat flowing into the interior oi'. the chargef" 'lhe regulation oi the furnace supply hy control of an induction regulator presents in itself very considerable advantages and may he utilized irrespective of the application of the other features of the invention described alcove.

A somewhat modiiied forni of the invention is shown in Figure 3 oi' the drawing. rlhe furnace is arranged similar to Figure l. The two three-phase resistor groups A and B of the furnace are controlled by "four threepole double-throw switches LK, L, lli, li', having switching members lil, K2, Ll, L2, L3, Ml, M2, M3, lll, N2, N3, and correspondingly marked contact members K1",K2, etc., respectively. Switch 2K may be thrown upwardly by energizing the actuating coil lc or downwardly 1oy energizing the actuating coil ls. The'sv/vitches lli, M, N inay he similarly controlled loy energizing the actuating coils ZI) ZIP? mi? .m/ 9%?? nl.

By throwing the switches K and L downward and switches ld and N upward, both resistor groups .spend B vare connected in delta. By leaving the switches K and L unchanged lout throwing the switches M and N downward,the two groups are connected in star, the second group B having an induction regulator l connected in the star point. ln

the next control .position the switches K andv L are thrown 'upward' thereby connecting the corresponding resistor elements of groups A and id in series.. The serielly-connected resistor elements may loe operated either in delta when the switch hl is thrown upward, or in star with the induction regulator in 'the star point lwhen said switch N is 'thrown downward. induction regulator may loe used to hoest the Voltage or to hucl the Voltage and is operatedhy a motor 5l which is' controlled from a suitable regulator 52 in accordance with the condition oi the thermocouples n or c, ein amplier 53 is connected,

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electric furnace having two resistor elements and means for connecting said resistor elements in delta or star connection with a source of current which comprises supplying said resistor elements in delta for rapidly 5 heating the furnace, re-connecting one of said elements in star independently of the other element, subsequently reconnecting said other of the elements in star independently of the first one of said elements so con nected, and gradually varying the temperature ofthe furnace while connected in star through the control of the voltage applied to one of the star connected resistor elements. In testimony whereof I haveV hereunto sub- Iscribed my name, at Zurich, Switzerland, this 27 day of May, A. D. 1927.

GGTTLIEB KELLER. 

